Turbulent drift-wave dynamics in a sheared magnetic field are studied using direct numerical simulations. Self-consistent nonadiabatic electron and parallel ion dynamics are both retained in a 2-D sheared-slab model. Magnetic shear causes division of the system into two physically distinct regions with differing cascade dynamics. In a hydrodynamic layer centered upon the mode resonant surface, linear coupling between the density and potential is weak, and the density gradient acts to force spontaneous nonlinear alignment of density fluctuations with the turbulent flows. Further away, shear-induced collisional dissipation constrains the density fluctuations to respond adiabatically, so that the density cannot vary onmore » flow streamlines. The dynamics of the interregion spatial energy flow leads to strong phase coherence between modes at scales larger than the hydrodynamic layer width. Concurrently, the alignment between flows and density fluctuations at scales comparable to the layer width becomes even stronger, increasing the energy input at those scales. This self-organizing tendency is sufficiently robust as to survive competition with a linear external drive. Because of its greater structural freedom, the full nonadiabatic system is much more likely than an adiabatic model with a linear density response to support saturated turbulence below the threshhold for linear instability.« less

Structure formation and self-organization in two-dimensional drift-wave turbulence show up in many different faces. Fluctuation data from a magnetized plasma are analyzed and three mechanisms transferring kinetic energy to large-scale structures are identified. Beside the common vortex merger, clustering of vortices constituting a large-scale strain field and vortex thinning, where due to the interactions of vortices of different scales larger vortices are amplified by the smaller ones, are observed. The vortex thinning mechanism appears to be the most efficient one to generate large scale structures in drift-wave turbulence. Vortex merging as well as vortex clustering are accompanied by strong energymore » transfer to small-scale noncoherent fluctuations (dissipation) balancing the negative entropy generation due to the self-organization process.« less